Penelitian ini mengkaji visibilitas Kastner sebagai alat prediksi Hilal dengan kelebihan mampu menilai kontras antara iluminasi Bulan dan kecerahan latar belakang, termasuk cahaya langit senja dan malam. pada penelitian ini, studi kasus yang diangkat adalah pada hasil laporan pengamatan Hilal di Balai Rukyat Condrodipo pada tahun 1443H-1445H, dengan rumusan masalah penelitian: (1) Bagaimana analisis visibilitas Kastner dalam memverifikasi hasil pengamatan Hilal di Balai Rukyat Condrodipo pada periode 1443H-1445H, (2) Bagaimana relevansi dan kontribusi visibilitas Hilal Kastner terhadap laporan pengamatan Hilal. Metode penelitian bersifat kualitatif dan dianalisis secara deskriptif dengan pengumpulan data melalui dokumentasi hasil pengamatan Hilal dan wawancara dengan Judhistira Aria Utama. Data yang diperoleh dianalisis dengan pendekatan sains dan statistik.
Hasil penelitian menunjukkan bahwa: (1) Ditemukan ketidaksesuaian antara prediksi Kastner pada 3 laporan pengamatan Hilal awal bulan pada tanggal 29 Syakban 1443H, 29 Safar 1444H, dan 29 Safar 1445H. Dari 19 pengamatan, dilakukan verifikasi menggunakan mata telanjang, teodolite, dan teleskop, dengan 16 pengamatan tidak relevan dan 25 relevan. Hasil verifikasi menunjukkan bahwa 16 laporan pengamatan berhasil dikonfirmasi menggunakan visibilitas Kastner menghasilkan visibilitas minimum seperti beda tinggi Matahari-Bulan 6o, elongasi 8o, dan umur Bulan 15 jam pasca konjungsi. Namun, parameter tersebut bersifat dinamis dan dapat berubah seiring bertambahnya data empirik lapangan. (2) Visibilitas Kastner memiliki relevansi sebagai bahan konfirmasi dan verifikasi hasil laporan pengamatan hilal untuk penentuan awal bulan kamariah, mengingat faktor ekstingsi, kecerahan langit, dan akuitas mata. Kontribusi visibilitas Kastner menjadi solusi dalam permasalahan awal bulan hijriah dengan keseimbangan antara data hisab astronomis dan pengamatan rukyat sesuai kaidah sainstifik, memperoleh hasil yang sesuai dengan fakta lapangan.

ABSTRACT:
This research examines the visibility of Kastner as a tool to predict the Hilal, with the advantage of being able to assess the contrast between the illumination of the Moon and the brightness of the background, including twilight and nighttime sky light. The case study in this research focuses on the observations of the Hilal at the Balai Rukyat Condrodipo during the period of 1443H-1445H, with the research questions formulated as follows: (1) How does the analysis of Kastner's visibility verify the observations of the Hilal at the Balai Rukyat Condrodipo during the period of 1443H-1445H? (2) What is the relevance and contribution of Kastner's Hilal visibility to the observations' report? The research method is qualitative and analyzed descriptively, collecting data through documentation of the Hilal observations and interviews with Judhistira Aria Utama. The obtained data is analyzed using a scientific and statistical approach.
The research findings indicate that: (1) Inconsistencies were found between Kastner's predictions and three initial reports of the Hilal on the 29th of Syakban 1443H, 29 Safar 1444H, and 29 Safar 1445H. Out of 19 observations, verification was conducted using the naked eye, a theodolite, and a telescope, with 16 observations deemed irrelevant and 25 relevant. The verification results show that 16 observation reports were successfully confirmed using Kastner's visibility, resulting in minimum visibility, such as a 6o difference between the Sun and the Moon, an elongation of 8o, and a Moon age of 15 hours post-conjunction. However, these parameters are dynamic and may change as empirical field data increases. (2) Kastner's visibility is relevant as a confirmation material and verification of the Hilal observation reports for determining the beginning of the lunar month, considering extinction factors, sky brightness, and visual acuity. The contribution of Kastner's visibility provides a solution to the issue of the beginning of the Hijri lunar month by balancing astronomical calculations and observational sightings according to scientific principles, achieving results in line with field facts.